The invention relates to methods and apparatus for performing broaching operations. In particular the invention concerns the performance of such methods on apparatus of the kind usually referred to as machining centers and to such apparatus adapted for performing the methods.
The normal arrangement for performing a broach operation is to mount a workpiece in position on a long bed broach machining center and to pull or push the broach tool through a roughed out slot or hole in the workpiece. The broach tool itself normally consists of a very stiff backing member or carrier carrying a plurality of cutting points one behind another and arranged so that they take progressively deeper cuts in the normal direction of travel.
Hitherto broaching operations have been carried out using special broach machines specifically designed for the purpose. Unfortunately this procedure suffers from several drawbacks: although the actual broach operation itself may be accurate, alignment errors are unavoidably introduced between preceding and succeeding operations and the broaching due to transfer of the workpiece from one machine to another. Also the zero position datum of the workpiece is inevitably lost, thus contributing a further source of potential error. Also time delays are incurred in transferring the workpiece from one machine to another and in machine setting up times. Thus, significant improvements may be obtained if broaching can be performed on the same machine as, say a grinding or milling operation, simply due to lost time saved and by preserving the zero datum.
The present invention seeks to overcome the aforementioned drawbacks by carrying out a broaching operation on a machine which is capable of performing other operations such as milling, drilling, turning, grinding, deburring and so on.
Therefore, according to one aspect of the present invention there is provided a broach tool comprising a very stiff backing member carrying a plurality of cutting points disposed to perform successive cutting operations as the broach tool is pushed through a workpiece.